The present invention relates to communications devices and more particularly to radio modems.
Radio receivers form an integral part of the radio modems used to transfer data between computers. Operating a radio receiver in proximity to a computing device, however, adversely affects the receiver performance. The square-wave clocks used throughout the computer frequently generate harmonic frequencies well into the radio frequency range. These harmonic frequencies are detected as narrow-band noise sources by the receiver and often have amplitudes large enough to completely overwhelm the incoming signal. Thus, these noise sources can prevent incoming data from reaching the receiving computer.
To compensate for this potential interference, systems including radio modems either shield the noise source from the receiver and/or employ data packet error correction and retry schemes to correct data corrupted by the interference. Shielding all of the circuitry in a computer system is complex, costly and adds weight to the device. Data correction methods are capable of correcting only a finite number of errors on either the packet or byte level. If a received packet of data contains too many errors to be corrected, the packet will not be acknowledged to the sending modem. The sending modem will then make another attempt at sending the message. The number of times the transmitting modem will "re-try" the transmission is defined by the network protocol and is also limited to a finite number. Thus, error detection and retry schemes alone are insufficient to ensure accurate exchange of data.